Field of the Invention
The present invention generally relates to wireless communication networks, such as cellular networks.
Overview of the Related Art
Evolution of cellular networks has experimented a significant growth in terms of spread and performance, and has recently brought inside 3GPP (“Third Generation Partnership Project”) to the definition of LTE (“Long Term Evolution”)/LTE-Advanced.
3GPP LTE/LTE-Advanced standard is conceived for allowing data to be high-speed conveyed between a fixed-location transceiver base station or node (e.g., eNodeB) radiating radio waves over a respective coverage area (cell) and user equipment (e.g., user terminals, such as cellular phones) within the coverage area.
Presently, cellular networks are seeing an increase in terms of number of new users and data throughput requirements. The ever increasing availability of new advanced user equipment, such as smartphones and tablets, has made available to the end users a huge number of client applications, many of them causing a frequent transmission and reception of data.
This implies that cellular networks should manage an ever increasing amount of signaling information. As it is known to those skilled in the art, with signaling information (or simply “signaling”) it is intended the information exchanged among user equipment and nodes of the cellular networks to ensure that user equipment are correctly linked to the cellular network. Signaling information concerns establishment, control and managing of the connection between a user equipment and the network, in contrast to user information, which concerns the actual content data exchanged between the user equipment and the network based on the specific type of service requested by the user equipment. The signaling information traffic increasing is caused by several factors, such as for example the “always-on” IP-connectivity required by smartphones, tablets and generally modern mobile devices, the widespread availability of applications for mobile devices (“Apps”) which require very frequent periodic updates, and the growth of machine-to-machine (M2M) devices.
As disclosed for example in Section 7.2, page 134 of “Introduction to 3G mobile communications” by Juha Korhonen, Artech House, 2nd edition, 2003, a cellular network may be regarded as formed by two sections, referred to as control plane (briefly, “C-plane”) and user plane (briefly, “U-plane”). The C-plane is the section of the cellular network mainly directed to manage the signaling information traffic, while the U-plane is the section of the cellular network that is mainly directed to manage the user information traffic.
In current cellular networks, signaling information traffic (or simply “signaling traffic”) and user information traffic (or simply “user traffic”) are usually managed as a single entity. In this case, the separation between the C-plane and the U-plane mainly occurs at logical level only. Each node of these cellular networks, regardless of the size of its corresponding coverage area, is configured to manage—within its coverage area and for each user equipment in said coverage area—both signaling and user traffic. Therefore, signaling information and user information may be transmitted/received by a same network node, for example by exploiting different time and/or frequency resources.
In order to improve the efficiency and the reliability of the cellular networks, studies have been recently carried out to provide network architectures in which the C-plane and the U-plane are decoupled both at logical and physical levels, to allow that signaling traffic travels separated from user traffic. For the sake of brevity, a cellular network of this type will be now on referred to as “decoupled network”. The nodes of a decoupled network may belong to a first category, associated to the C-plane, or to a second category, associated to the U-plane. The nodes of the first category, also referred to as “C-plane nodes”—usually implemented by the macro nodes of the network—are responsible for the C-plane coverage, and are specialized to manage signaling traffic. The nodes of the second category, also referred to as “U-plane nodes”—usually implemented by the small nodes of the network—are instead responsible for the U-plane coverage, and are specialized to mainly manage user traffic. The coverage area size of each C-plane node is in general larger than the coverage area size of each U-plane node. The coverage areas of all the C-plane nodes of the decoupled network cover (with possible overlapping) portions of the territory in which the decoupled network is located. U-plane nodes are located within the coverage area of each C-plane node of the decoupled network, with the coverage areas of said U-plane nodes that cover (with possible overlapping) at least portions of the territory covered in turn by the coverage area of the corresponding C-plane node. From now on, when a user equipment is said to be within the coverage area of a C-plane node, it means that said user equipment is under the control of said C-plane node and is capable of exchanging signaling traffic therewith. Similarly, when a user equipment is said to be within the coverage area of a U-plane node, it means that said user equipment is in condition to establish a link to said U-plane node and is capable of exchanging user traffic therewith.
The decoupling between the C-plane and the U-plane coverage has been considered as a potential solution within the “Small Cells Enhancements” Study Item of the 3GPP Release 12 specification activity. In 3GPP context, several contributions have been produced by 3GPP members proposing slightly different views on this issue.
For example, in order to provide high throughputs in a flexible and energetically efficient way, in the document RWS-120019, “LTE Release 12 and Beyond” (3GPP RAN WS on Rel-12 and onwards, Ljubljana, Slovenia, 11-12 Jun. 2012) it is proposed the introduction of so-called “Phantom Cells” operating on a high frequency carrier (in the proposed example, at 3.5 GHz) and dedicated to serve the U-plane, leaving the management of the C-plane to macro cells having wider coverage areas. The actual degree of separation between the C-plane and the U-plane obtainable with said architecture is currently under discussion (see for example R2-131329, “Necessity of C-plane architecture enhancements for dual connectivity”, 3GPP TSG-RAN2 #81bis, Chicago, USA, 15-19 Apr. 2013).
Similar solutions have been proposed in the document RWS-120003, “LTE Release 12 and Beyond” (3GPP RAN WS on Rel-12 and onwards, Ljubljana, Slovenia, 11-12 Jun. 2012). Said solutions provide for small cells—identified by the terms “Virtual cells” or “Soft Cells”—dedicated to the U-plane that are deployed within the area covered by wider macro cells dedicated to the C-plane. In order to guarantee the off-loading of high volumes of user traffic data with minimal signaling overhead, according to these solutions the small cells exploit carriers (called “booster carriers”) for the U-plane different from the carriers (called “anchor carriers”) exploited by the macro cells for the C-plane.
According to what proposed in the document RWS-120047, “LTE Release 12 and Beyond” (3GPP RAN WS on Rel-12 and onwards, Ljubljana, Slovenia, 11-12 Jun. 2012), macro cells should be designed to mainly take care of the C-plane, while small cells having smaller coverage area should be designed to improve system capacity mainly taking care of the U-plane and to keep signaling functions for legacy terminals only.
The same concept has been proposed in the document RWS-120006, “Views on Rel-12 and onwards for LTE and UMTS”, (3GPP RAN WS on Rel-12 and onwards, Ljubljana, Slovenia, 11-12 Jun. 2012) introducing the concept of “Low Power Nodes”. According to this solution, a reference macro cell is designed to give “assistance” to a plurality of low power nodes by means of coordination mechanisms. A similar concept is also proposed in the document RWS-120004, “LTE Release 12 and Beyond”, (3GPP RAN WS on Rel-12 and onwards, Ljubljana, Slovenia, 11-12 Jun. 2012). The “Amorphous Cells” introduced in the document RWS-120034, “LTE Release 12 and Beyond”, (3GPP RAN WS on Rel-12 and onwards, Ljubljana, Slovenia, 11-12 Jun. 2012) are low power nodes coordinated by macro cells.
EP 2533595 discloses a concept for interference coordination in a heterogeneous network with an apparatus for a mobile transceiver, an apparatus for a macro base station transceiver and an apparatus for a small base station transceiver. The mobile transceiver is adapted for communicating with the macro base station transceiver and is interfered by the small base station transceiver. The mobile transceiver is associated with the macro base station transceiver. The small base station transceiver is configured for denying an association request with the mobile transceiver. The apparatus for the mobile transceiver comprises means for measuring a radio signal transmitted by the small base station transceiver to obtain a small cell measurement result and means for providing information on the small cell measurement result to the macro base station transceiver. The apparatus for the macro base station transceiver comprises means for receiving information on a small cell measurement result from the mobile transceiver, means for determining a subset of the plurality of radio resources to be restricted for the small base station transceiver based on the information on the small cell measurement result and means for communicating information on the subset of radio resources to the small base station transceiver. The apparatus for the small base station transceiver comprises means for obtaining information on a subset of the plurality of radio resources to be restricted for the small base station transceiver from the macro base station transceiver and means for allocating radio resources for data transmission to the mobile transceiver based on the information on the subset of the plurality of radio resources.
U.S. Pat. No. 6,973,054 discloses a method in a communication system of transferring control of a user-plane entity from a first control-plane entity to a second control-plane entity. The user-plane entity sends a set of identifying parameters to the first control-plane entity, which subsequently sends the set of identifying parameters to the second control-plane entity. The second control-plane entity determines if it can control the user-plane entity. If the second control-plane entity can control the user-plane entity, then the second control-plane entity sends an indication to the user-plane entity that a change in control-plane entities has occurred and that at least some resources of the user-plane entity that were controlled by the first control-plane entity are to be controlled by the second control-plane entity. The resources may be allocated to a mobile terminal and the change in control entity may be the result of a change in location of the mobile terminal.
WO2012004663 discloses a method and an eNB for power saving in a heterogeneous network. When the eNB serving the overlay capacity boosting cell does not detect any user equipments accessing the overlay capacity boosting cell, it turns off its downlink transmission; when the eNB serving the overlay capacity boosting cell detects that the user equipment is approaching its coverage area, it turns on its downlink transmission. The eNB serving the overlay capacity boosting cell has two working state, normal transmitting and receiving state, and receiving state, and the eNB serving the overlay capacity boosting cell autonomously turns on and turns off the downlink transmission according to the detecting results of itself, instead of relying on the intervening or indication from the eNB serving the underlay basic coverage cell, so as to achieve the aim of power saving.
WO2012166975 discloses a hybrid user equipment and small-node device data offloading architecture. In this hybrid architecture, the small-node device includes a backhaul link to a telecommunication network and/or the Internet. The user equipment can send and receive data through the small-node device using the backhaul link.